Apparatus and methods for magnetic control of radiation electron beam

ABSTRACT

Apparatus and methods for controlling a radiotherapy electron beam. Exemplary embodiments provide for focusing the electron beam at different depths by altering parameters of a plurality of magnets. Exemplary embodiments can also provide for focusing the electron beam at different depths while maintaining the energy level of the electron beam at a consistent level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/331,459, filed Mar. 7, 2019, which is a national phase applicationunder 35 U.S.C. § 371 of International Application No.PCT/US2017/050066, filed Sep. 5, 2017, which claims priority to U.S.Provisional Patent Application No. 62/385,346, filed Sep. 9, 2016, theentire contents of each of which are incorporated herein by reference.

BACKGROUND INFORMATION

Electron beam radiation therapy utilizes ionizing radiation, typicallyas part of cancer treatment to destroy malignant cells. Radiationtherapy may be curative in a number of types of cancer if they arelocalized to one area of the body. It may also be used as part ofadjuvant therapy to prevent tumor recurrence after surgery to remove aprimary malignant tumor. For example, electron beam radiation therapymay be used as part of adjuvant therapy in the early stages of certaintypes of cancer such as breast cancer.

Radiation therapy is commonly applied to the cancerous tumor due to itsability to control cell growth. Ionizing radiation works by damaging theDNA of cancerous tissue leading to cellular death. To reduce exposure ofhealthy tissues (e.g. tissues which radiation must pass through to treatthe tumor), radiation beams can be aimed from different angles tointersect at the tumor.

Electron beam radiation therapy is currently used to direct radiation toa target region (e.g. a region containing the tumor) to destroy cellswithin the target region. Typical electron systems are limited in thedepth that a target region can be successfully treated. In addition,typical systems do not provide dynamic control of the radiation depthand can direct unwanted radiation to healthy tissues surrounding thetarget region.

For example, with existing systems the beam energy is manually selectedto control the depth of radiation penetration up to a peak dose depth ofapproximately 3 cm (determined by currently commercially availablemaximum clinical electron beams energy of 20 MeV). In such systems thebeam energy is increased in order to increase the depth of radiationpenetration. This provides for higher radiation levels for tissue at ornear the surface, and can lead to unwanted excessive radiation exposureto surrounding healthy tissue.

Accordingly, a need exists for new radiation therapy apparatus andmethods that provide greater control of radiation dosage levels atvarying depths and minimize radiation exposure to surrounding healthytissues.

SUMMARY

As explained in more detail below, exemplary embodiments of the presentdisclosure enable improvements in many aspects of electron beamradiation therapy as compared to current apparatus and methods.

Exemplary embodiments of the present disclosure include an electron beamdelivery and control system using very high energy electrons (VHEE) toproduce a localized focal spot of high radiation dosage within thetarget volume. Exemplary embodiments are able to control the location ofthe focal spot through a technique referred to herein as magneticallyoptimized very high energy electron treatment (MOVHEET).

Apparatus incorporating MOVHEET techniques can be dynamically controlledto produce a distribution of radiation dosage within a target region(e.g. a tumor volume) that is higher than surrounding normal tissue.This ability can result in greater normal tissue sparing and a largerdegree of radiation control around the tumor volume. Exemplaryembodiments include the ability to dynamically focus an electron beam of50-250 megaelectron volts (MeV) to a focal spot at a desired targetdepth. As used herein, the term “depth” when used in reference to thefocal spot refers to a dimension measured parallel to the electron beam(e.g. parallel to the primary axis of the beam prior to entering themagnetic control apparatus). The desired target depth can be determinedby a radiation treatment plan dose distribution, where the output of thefocusing system is a beam with optimized symmetry and a focusing anglethat results in a low beam density at the target surface producing lowentrance dose.

Methods for dynamically controlling the focal spot depth of the electronfocusing system can include the use of magnetic fields outside thetarget volume to alter the electron trajectories to produce the desiredbeam behavior.

One embodiment of the focusing system utilizes quadrupole magneticfields which are produced by a magnet having four inwardly directedpoles such that each adjacent pole carries a magnetic field of oppositepolarity. Current-carrying coils can be arranged in such a way toproduce a magnetic field inside the ferromagnetic magnet material, wherethe strength of the magnetic quadrupole field may be adjusted by varyingthe coil current. This type of magnet design is referred to asiron-dominated.

Another embodiment of a quadrupole magnet is based on a coil-dominateddesign where the current-carrying coils are designed in such a way suchthat the magnetic multipole field experienced by the charged particlebeam is produced directly by the coils themselves without the use of aferromagnetic core. Varying the current in the coils adjust strength ofthe magnetic field.

A quadrupole magnetic field has the effect of defocusing a chargedparticle beam in one plane while focusing the beam in the orthogonalplane. This can allow for overall focusing in both planes beingaccomplished with a combination of quadrupole magnets whose currents,positions, and other magnet parameters have been chosen to produce thedesired beam. A variety of exit beam shapes may be used, and certainconfigurations of quadrupoles may be used to generate symmetric beams.

In one such configuration, a combination of three collinear quadrupolemagnets can produce symmetrically focused beams for parallel incomingelectron beams. Such systems can also provide for stigmatic focusing ofa diverging beam where the beam focal spot may be adjusted by varyingthe quadrupole magnet strengths (alone or in conjunction with otherparameter alterations).

In another such configuration, a combination of two collinear quadrupolemagnets can be use to produce output beams with an oblong shape that maybe ideal for certain dose distributions that have strict spatialtolerances due to surrounding critical structures. The use of quadrupolesystems with two or three quadrupoles allows for the user to choose theappropriate focusing distribution based on the target area.

For example, in order to attain the desired depth dose distribution forthe range of depths typically used for clinical treatment (e.g. 0-35centimeters), the quadrupole separation distances and triplet positioncan be varied to achieve the optimal treatment beam. During operation, aquadrupole magnet system can produce a focused beam when the quadrupolesare operated under a specific set of conditions determined by thesolution to a system of differential equations that govern thetrajectories of the electrons within the field regions.

In exemplary embodiments, a control system for the magnet parameterstakes the dose distribution from the treatment planning software anduses an algorithm to calculate the necessary focusing system parametersto produce the desired beam trajectories.

The beam can also be scanned laterally by means of orthogonal dipolefields which produce a uniform offset to the beam in their respectivedirections to produce a three-dimensional dose distribution. Otherembodiments may mechanically move the focusing system to produce athree-dimensional dose distribution. The lateral scanning parameters canbe included in the beam control system and determined by the treatmentplanning software.

For focusing systems using diverging input beams, the beam divergenceand origination point are also variables that can be determined by thecontrol system algorithm. As an example, a pencil beam may be madedivergent by the use of a scattering foil designed to produce a uniquedivergence pattern, where the divergent beam is then passed through acollimator in order to restrict the divergence angle for input into thequadrupole focusing system. The relative locations between thescattering foil, collimator, and quadrupole entrance are unique for aparticular exit beam and can be determined along with the quadrupolesettings.

It should be noted that magnetic fields can have inherentinconsistencies or errors that can translate into nonuniformities in thefocused electron beam. Careful consideration for such inconsistenciesmay be taken into account with the use of sextupole and octupoleconfigurations, for example, to compensate for various geometrical andchromatic inconsistencies. One embodiment of the focusing system may usea quadruplet of quadrupole magnets coincident with three interspersedoctupole magnets to produce a focused beam with geometrical aberrationcorrection.

In certain embodiments, an algorithm may be used to solve for the magnetparameters that produce a symmetrically focused beam whereinconsistencies introduced by the quadrupoles have been compensated forby the octupole magents producing a higher quality dose distribution inthe target volume. The control system can dynamically adjust theparameters to optimize the beam determined by the treatment planningsystem. It is understood that the magnet configurations disclosed hereinare merely exemplary, and that other combinations of magnets may be usedto correct for other magnet-induced inconsistencies.

Certain embodiments may dynamically control beam depth by utilizing aposterior solenoidal magnet to produce a magnetic field gradient withinthe target volume such that the electrons reverse direction at a depthdetermined by the magnetic field strength. An anterior solenoidal magnetmay be used in conjuction with the posterior magnet to modify themagnetic field in the target volume and enhance the dose deposition. Thelocalized high dose region depth may be controlled with a control systemdesigned to adjust the solenoid currents based on the desired dosedistribution.

Exemplary embodiments include an apparatus for controlling aradiotherapy electron beam, where the apparatus comprises: an electronbeam generator configured to generate an electron beam; a plurality ofmagnets producing a plurality of magnetic fields configured to focus theelectron beam to a focal spot; and a control system configured to alterone or more parameters of the plurality of magnets to move the focalspot from a first location to a second location, where the firstlocation is located at a first depth within a target region and thesecond location is located at a second depth within the target region.

In certain embodiments, the target region is below an epidermal surfaceof a subject; the first location or the second location is at a depthbetween 0 and 50 centimeters from the epidermal surface. In particularembodiments, the electron beam has a energy of between 50 and 250megaelectron volts (MeV). In some embodiments, the energy of the beam isnot modulated when the focal spot is moved from the first location tothe second location. In specific embodiments, the plurality of magnetscomprise a plurality of collinear multipole magnets. In certainembodiments, the plurality of collinear multipole magnets comprises atleast two collinear quadrupole magnets.

In particular embodiments, the one or more parameters of the pluralityof magnets comprises a separation distance between the plurality ofcollinear multipole magnets; and the control system is configured toalter the separation distance between the plurality of collinearmultipole magnets. In some embodiments, the plurality of magnetscomprise an anterior lens magnet, a posterior reflective magnet, and aplurality of radial focal magnets. In specific embodiments, theplurality of magnets comprise electromagnets; the one or more parametersof the plurality of magnets comprises an electrical current through theelectromagnets; and the control system is configured to alter theelectrical current through the electromagnets. In certain embodiments,the electromagnets are iron-dominated or coil dominated superconductingelectromagnets.

In particular embodiments, the plurality of magnetic fields areconfigured to focus the electron beam at a convergence angle of between50 and 500 mrad. In some embodiments, the plurality of magnetic fieldsare configured to focus the electron beam at a convergence angle ofbetween 200 and 400 mrad. In specific embodiments, the control systemcomprises an algorithm to calculate the one or more parameters of theplurality of magnets. In certain embodiments, the control systemreceives input from a treatment planning software program configured tocalculate a dose distribution. In particular embodiments, the focal spotcomprises a maximum electron dose concentration.

Exemplary embodiments include a method of controlling a radiotherapyelectron beam, where the method comprises: generating an electron beam;directing the electron beam through a plurality of magnetic fieldsproduced by a plurality of magnets; focusing the electron beam to afocal spot with the plurality of magnetic fields; and altering one ormore parameters of the plurality of magnets to move the focal spot froma first location to a second location where the first location islocated at a first depth within a target region and the second locationis located at a second depth within the target region.

In certain embodiments, the target region is below an epidermal surfaceof a subject; and the first location or the second location is at adepth between 0 and 50 centimeters from the epidermal surface. Inparticular embodiments, the electron beam has a power of between 50megaelectron volts and 250 megaelectron volts. In some embodiments, thepower of the beam is not modulated when the focal spot is moved from thefirst location to the second location. In specific embodiments, theplurality of magnets comprise a plurality of collinear multipolemagnets. In certain embodiments, the plurality of collinear multipolemagnets comprises at least three collinear quadrupole magnets.

In particular embodiments, the one or more parameters of the pluralityof magnets comprises a separation distance between the plurality ofcollinear multipole magnets; and the control system is configured toalter the separation distance between the plurality of collinearmultipole magnets. In some embodiments, the plurality of magnetscomprise an anterior lens magnet, a posterior reflective magnet, and aplurality of radial focal magnets. In specific embodiments, theplurality of magnets comprise electromagnets; the one or more parametersof the plurality of magnets comprises an electrical current through theelectromagnets; and the control system is configured to alter theelectrical current through the electromagnets.

In certain embodiments, the plurality of magnetic fields are configuredto focus the electron beam at a convergence angle of between 100 and 500mrad. In particular embodiments, the plurality of magnetic fields areconfigured to focus the electron beam at a convergence angle of between200 and 400 mrad. In some embodiments, the control system comprises analgorithm to calculate the one or more parameters of the plurality ofmagnets. In specific embodiments, the control system receives input froma treatment planning software program configured to calculate a dosedistribution. In certain embodiments, the focal spot comprises a maximumelectron dose concentration.

Exemplary embodiments include an apparatus for controlling aradiotherapy electron beam, where the apparatus comprises: an electronbeam generator configured to generate an electron beam with a powerbetween 50 megaelectron volts and 250 megaelectron volts; a plurality ofmagnets configured to focus the electron beam at a focal spot; and acontrol system configured move the focal spot from a first location at afirst depth to a second location at a second depth, wherein the power ofthe electron beam is maintained at a consistent level when the focalspot is moved from the first location to the second location.

In certain embodiments, the first location and the second location arelocated within a target region. In particular embodiments, the targetregion is below an epidermal surface of a subject; and the firstlocation or the second location is at a depth between 10 and 20centimeters from the epidermal surface. In some embodiments, the controlsystem is configured to alter one or more parameters of the plurality ofmagnets to move the focal spot from the first location to the secondlocation. In specific embodiments, the control system comprises analgorithm to calculate the one or more parameters of the plurality ofmagnets.

In certain embodiments, the control system receives input from atreatment planning software program configured to calculate a dosedistribution. In particular embodiments, the plurality of magnetscomprise a plurality of collinear multipole magnets. In someembodiments, the plurality of collinear multipole magnets comprises atleast three collinear quadrupole magnets. In specific embodiments, theone or more parameters of the plurality of magnets comprises aseparation distance between the plurality of collinear multipolemagnets; and the control system is configured to alter the separationdistance between the plurality of collinear multipole magnets.

In certain embodiments, the plurality of magnets comprise an anteriorlens magnet, a posterior reflective magnet, and a plurality of radialfocal magnets. In particular embodiments, the plurality of magnetscomprise electromagnets; the control system is configured to alter oneor more parameters of the plurality of magnets to move the focal spotfrom the first location to the second location; the one or moreparameters of the plurality of magnets comprises an electrical currentthrough the electromagnets; and the control system is configured toalter the electrical current through the electromagnets.

In particular embodiments, the plurality of magnets are configured tofocus the electron beam at a convergence angle of between 100 and 500mrad. In some embodiments, the plurality of magnets are configured tofocus the electron beam at a convergence angle of between 200 and 400mrad. In specific embodiments, the focal spot comprises a maximumelectron dose concentration.

Certain embodiments include a method of controlling a radiotherapyelectron beam, where the method comprises: generating an electron beamhaving a power between 50 megaelectron volts and 250 megaelectron volts;focusing the electron beam to a focal spot with a plurality of magnets;and moving the focal spot from a first location at a first depth to asecond location at a second depth while maintaining the power of theelectron beam at a consistent level.

In particular embodiments, the first location and the second locationare located within a target region. In certain embodiments, the targetregion is below an epidermal surface of a subject; the first location orthe second location is at a depth between 10 and 20 centimeters from theepidermal surface. In some embodiments, moving the focal spot from afirst location at a first depth to a second location at a second depthcomprises altering one or more parameters of the plurality of magnets.In specific embodiments, the control system comprises an algorithm tocalculate the one or more parameters of the plurality of magnets. Inparticular embodiments, the control system receives input from atreatment planning software program configured to calculate a dosedistribution. In certain embodiments, the plurality of magnets comprisea plurality of collinear multipole magnets. In some embodiments, theplurality of collinear multipole magnets comprises at least threecollinear quadrupole magnets.

In specific embodiments, the one or more parameters of the plurality ofmagnets comprises a separation distance between the plurality ofcollinear multipole magnets; and altering one or more parameters of theplurality of magnets comprises altering the separation distance betweenthe plurality of collinear multipole magnets. In certain embodiments,the plurality of magnets comprise an anterior lens magnet, a posteriorreflective magnet, and a plurality of radial focal magnets. Inparticular embodiments, the plurality of magnets compriseelectromagnets; and moving the focal spot from a first location at afirst depth to a second location at a second depth comprises altering anelectrical current through the electromagnets.

In certain embodiments, the plurality of magnets are configured to focusthe electron beam at a convergence angle of between 100 and 500 mrad. Inparticular embodiments, the plurality of magnets are configured to focusthe electron beam at a convergence angle of between 200 and 400 mrad. Insome embodiments, the focal spot comprises a maximum electron doseconcentration.

In the following, the term “coupled” is defined as connected, althoughnot necessarily directly, and not necessarily mechanically.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more” or “at leastone.” The terms “about”, “substantially” and “approximately” mean, ingeneral, the stated value plus or minus 5%. The use of the term “or” inthe claims is used to mean “and/or” unless explicitly indicated to referto alternatives only or the alternative are mutually exclusive, althoughthe disclosure supports a definition that refers to only alternativesand “and/or.”

The terms “comprise” (and any form of comprise, such as “comprises” and“comprising”), “have” (and any form of have, such as “has” and“having”), “include” (and any form of include, such as “includes” and“including”) and “contain” (and any form of contain, such as “contains”and “containing”) are open-ended linking verbs. As a result, a method ordevice that “comprises,” “has,” “includes” or “contains” one or moresteps or elements, possesses those one or more steps or elements, but isnot limited to possessing only those one or more elements. Likewise, astep of a method or an element of a device that “comprises,” “has,”“includes” or “contains” one or more features, possesses those one ormore features, but is not limited to possessing only those one or morefeatures. Furthermore, a device or structure that is configured in acertain way is configured in at least that way, but may also beconfigured in ways that are not listed.

Other objects, features and advantages of the present invention willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and the specificexamples, while indicating specific embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will beapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE FIGURES

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The present disclosure may be better understood by referenceto one or more of these drawings in combination with the detaileddescription of specific embodiments presented herein.

FIG. 1 displays a schematic of an apparatus for controlling aradiotherapy electron beam according to exemplary embodiments of thepresent disclosure.

FIG. 2 displays a perspective view of an arrangement of magnets in theembodiment of FIG. 1

FIG. 3 displays a simulated dose distribution plot in the X-Z plane ofthe embodiment of FIG. 1.

FIG. 4 displays a simulated dose distribution plot in the Y-Z plane ofthe embodiment of FIG. 1.

FIG. 5 displays a graph of a simulated percent dose distribution curvesfor the embodiment of FIG. 1 compared to an unfocused electron beam.

FIG. 6 displays a schematic of an apparatus for controlling aradiotherapy electron beam according to exemplary embodiments of thepresent disclosure.

FIG. 7 illustrates a graph of simulated percent depth dose curves fordifferent configurations of the embodiment of FIG. 1.

FIG. 8 illustrates a Monte Carlo calculation of a composite dosedistribution from multiple electron beams focused on a prostate CT(computed tomography) image for the embodiment of FIG. 6.

FIG. 9 illustrates a Monte Carlo calculation of a composite dosedistribution from multiple electron beams focused on a prostate CT(computed tomography) image for the embodiment of FIG. 6.

FIG. 10 illustrates a graph of simulated percent depth dose curves fordifferent configurations of the embodiment of FIG. 6.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring initially to FIG. 1, an apparatus 100 for controlling aradiotherapy electron beam is shown. In this embodiment, apparatus 100comprises an electron beam generator 150 configured to generate anelectron beam 155. Apparatus 100 further comprises a plurality ofmagnets 105 that includes collinear multipole magnets.

In this embodiment, magnets 105 include a first quadrupole magnet 101, asecond quadrupole magnet 102 and a third quadrupole magnet 103. Firstquadrupole magnet 101 comprises first pole 111, second pole 112, thirdpole 113 and fourth pole 114. It is understood that second quadrupolemagnet 102 and third quadrupole magnet 103 also comprise four poles (notlabeled in the figures for purposes of clarity). A top perspective viewof magnets 105 is shown in FIG. 2.

During operation of apparatus 100, magnets 105 produce a plurality ofmagnetic fields configured to focus electron beam 155 and provide amaximum electron dose concentration at a focal spot in a target region.Referring specifically to FIGS. 3 and 4, simulated dose distributionplots are shown for apparatus 100 in the X-Z plane (FIG. 3) and Y-Zplane (FIG. 4). Dose distributions where calculated using the MonteCarlo calculation code FLUKA© which is a general purpose code forsimulating the interactions of energetic particles in matter. See “TheFLUKA Code: Developments and Challenges for High Energy and MedicalApplications” T. T. Böhlen, F. Cerutti, M. P. W. Chin, A. Fassó, A.Ferrari, P. G. Ortega, A. Mairani, P. R. Sala, G. Smirnov and V.Vlachoudis, Nuclear Data Sheets 120, 211-214 (2014); see also “FLUKA: amulti-particle transport code” A. Ferrari, P. R. Sala, A. Fassó, and J.Ranft, CERN-2005-10 (2005), INFN/TC_05/11, SLAC-R-773. FIGS. 3 and 4were produced by tracking 2.5×10⁵ with a minimum step size of 0.05 cm,charged particle cutoff energy of 10 keV, and dose binning grid size of1 mm. In this example, electron beam 155 is a 100 megaelectron volt(MeV), 5 centimeter radius electron beam. Electron beam 155 is shownpassing through 100 centimeters of air and incident on a water phantom(at Z dimension 0 centimeters, corresponding to an epidermal surface ofa subject). In the illustrated embodiment, magnets 105 are configured asa quadrupole triplet and function as a symmetric uniform focusing lens.

As shown in FIG. 3, first quadrupole magnet 101 focuses electron beam155 in the X-Z plane, while second quadrupole magnet 102 defocuseselectron beam 155, and third quadrupole magnet 103 focuses electron beam155. As shown in FIG. 4, magnets 101, 102 and 103 perform the inverseoperations on electron beam 155 in the Y-Z plane. In particular, firstquadrupole magnet 101 defocuses beam 155 in the Y-Z plane, while secondquadrupole magnet 102 focuses electron beam 155, and third quadrupolemagnet 103 defocuses electron beam 155.

As shown in FIGS. 3 and 4, magnets 105 may be configured to focuselectron beam 155 and provide a maximum electron dose concentration at afocal point 125. As explained further below, during operation controlsystem 190 (shown in FIG. 1) can alter one or more parameters of magnets105 to move focal spot 125 to different depths within a target region inthe Z-plane. In exemplary embodiments, the power of electron beam 155 isnot modulated when focal spot 125 is moved to different depths within atarget region.

For example, control system 190 may control the position of individualmagnets in the group of magnets 105 in order to alter the separationdistance between the magnets. In particular, control system 190 mayalter the separation distance between first quadrupole magnet 101 andsecond quadrupole magnet 102. Control system 190 may also alter theseparation distance between second quadrupole magnet 102 and thirdquadrupole magnet 103.

The separation distance between magnets 101, 102 and 103 may be alteredby any one of suitable mechanisms, including for example, one or morelinear actuators. For example, as shown in FIG. 1, control system 190can control the position of magnets 101, 102 and 103 via linearactuators 131, 132 and 133 respectively. By adjusting the position ofeach magnet 101, 102 and 103, the separation distances between themagnets can be altered. The alteration of the separation distancesbetween magnets in the group of magnets 105 affects the focusing ofelectron beam 155 and convergence angle A, shown in FIG. 4.

As convergence angle A is increased, focal spot 125 is moved closer tomagnets 105. Conversely, as the separation distance between magnets 105is controlled to decrease convergence angle A, focal spot 125 is movedfarther from magnets 105. In certain embodiments, apparatus 100 canincrease convergence angle A up to values of approximately 400milliradians. This can allow focal spot 125 to be moved within thetarget region, which is typically between 0 and 35 centimeters from thesurface. It is understood that a similar convergence angle is present inthe X-Z plane of FIG. 3. The convergence angle present in FIG. 3 is notlabeled for purposes of clarity.

In other embodiments, control system 190 may control differentparameters in order to control electron beam 155 and focal spot 125. Forexample, in certain embodiments magnets 105 may comprise electromagnetsand control system 190 can be configured to alter the electrical currentthrough the electromagnets. Similar to the magnet separation distance,altering the electrical current through each of magnets 101, 102 and 103can also affect convergence angle A and the position of focal spot 125.Accordingly, the alteration of magnet parameters (e.g. magnet separationdistance or electrical current) can change the depth of focal spot 125by allowing focal spot 125 to be moved closer to and farther frommagnets 105 in an axial direction (e.g. collinear with electron beam155).

The ability to control convergence angle A and the location of focalspot 125 via magnetic parameters can provide numerous advantages. Forexample, the radiation dose can be reduced in regions outside of thetarget region. In particular, the ability to create a higher convergenceangle can provide a larger cross section of beam 155 at the skin surfaceas compared to the cross section at focal spot 125. Particularembodiments may be capable of producing surface entrance doses as low asfifteen percent of the maximum dose at the focal spot 125, as opposed totypical current technologies that provide surface doses of approximatelyeighty or ninety percent of the maximum dosage. The ability to controlthe axial depth location of the focal spot and minimize radiation dosagelevels to healthy tissues outside the target region can improve patientoutcomes and reduce recovery times.

Furthermore, exemplary embodiments also provide the ability to controlthe depth of the radiation dose peak at focal point 125 within a targetregion without modulating the energy of beam 155. Current electrontherapy technology typically varies the energy of the electron beam toadjust the depth of penetration, which is done manually and is notsuited for dynamic control of the dosage level. For example, changingthe energy of the beam to adjust the depth of penetration does not allowfor independent control of focal spot depth and radiation levels.

In contrast, exemplary embodiments of the present disclosure areconfigured to penetrate the full clinical range of patient thicknessesand then use the magnetic system parameters to produce a high dose focalregion in the target which may be moved throughout the target depth. Thetarget depth can be controlled by parameters (e.g. magnet current and/orpositions) other than electron beam energy levels.

As a result of dose peak depth control as disclosed herein, beams ofvarying dose peak depths may be superimposed to produce a region ofconstant dose over a region of depth within the patient corresponding toa tumor or treatment site.

FIG. 5 illustrates a graph of a simulated percent dose distributions for140 MeV electron beams on water for a 5 centimeter radius circular beam.In one plot of FIG. 5, the electron beam is not focused, while in theother plot the same beam is focused with a collinear quadrupole magnetconfiguration as shown in FIGS. 1 and 2. As shown in FIG. 5, the percentdose at the surface (e.g. depth of 0 cm) is substantially reduced forthe focused beam as compared to the unfocused beam. The focused beamprovides a dose at the surface of between 20 and 30 percent of themaximum dose, while the unfocused beam provides a surface dose ofbetween 70 and 80 percent of the maximum. FIG. 5 also illustrates thefocused beam provided a maximum dose at slightly less than 15 cm depth.

Other embodiments may comprise a different configuration of magnets thanthose previously shown and described. For example, referring now to FIG.6, an apparatus 200 comprises a plurality of magnets 205 that are notcollinear and are configured to control an electron beam 255. In thisembodiment, magnets 205 are configured as solenoidal electromagnets andcomprise an anterior lens magnet 201, a posterior reflective magnet 202,and a plurality of radial focal magnets 203, 204, 206 and 207.

During operation of apparatus 200, a control system 290 can controlparameters of magnets 205 to focus beam 255 at different depths, in amanner similar to the previously-described embodiments. For example,control system 290 can control an electrical current through each ofmagnets 201-204 and 206-207. Control system may also be configured tocontrol the position of magnets 201-204 and 206-207 so that theseparation distance between each of the magnets is altered to change thefocal spot (not shown in FIG. 6 for purposes of clarity) of beam 255.

In the configuration shown in FIG. 6, anterior lens magnet 201 is theprimary source of focusing. Radial focal magnets 203, 204, 206 and 207produce a magnetic field within the target that modifies the anteriorlens magnet 201 field and provides additional focusing. The plane ofradial focal magnets 203, 204, 206 and 207 can be adjusted based on thetreatment depth. Posterior reflective magnet 202 produces a magneticfield gradient such that electrons are reflected at a depth dependent onthe magnetic field strength of magnet 202, resulting in a radiation doseconfined to a desired depth.

FIG. 7 illustrates a graph of simulated percent depth dose curves for100 MeV, 5 cm radius electron beams incident on a water phantom, wherethe beam has been focused using the FIG. 6 configuration with differentdepths of the magnetic plane as defined by the in-plane magnets 203,204, 206, and 207. As shown in FIG. 7, the different depths magneticplanes corresponds to a shift in the dose peak to different depths. The40 cm magnetic plane has a maximum dose peak at approximately 16 cm, the35 cm magnetic plane has a maximum dose peak at approximately 13.5 cm,the 30 cm magnetic plane has a maximum dose peak at approximately 11.5cm, and the 25 cm magnetic plane has a maximum dose peak atapproximately 8.5 cm. For comparison, the percent depth dose curve for a5 cm radius circular beam of 20 MeV electrons without any focusingmagnetic fields is shown. As shown in FIG. 7, the surface dose of theunfocused 20 MeV beam is between 80 and 90 percent, while the focusedbeams have a surface dose between 10 and 20 percent.

FIG. 8 illustrates a Monte Carlo calculation of a composite dosedistribution from five focused electron beams of varying energies on aprostate CT (computed tomography) image using the magnet configurationshown in FIG. 6. FIG. 9 illustrates a Monte Carlo calculation of acomposite dose distribution from 10 focused electron beams of varyingenergies utilizing a form of “dose painting” (e.g. altering the depth ofa focal spot for each of the beams). This technique can be been used toincrease the high dose coverage throughout the prostate using the magnetconfiguration shown in FIG. 6.

FIG. 10 illustrates a graph of the percent dose versus depth fordifferent configurations of the embodiment shown in FIG. 6 utilizingradial focal magnets with an anterior lens magnet and a posteriorreflective magnet. The graphs include a 25 centimeter magnetic planeconfiguration, a 40 centimeter magnetic plane configuration with theintensities of each distribution optimized to produce a simulated spreadout Bragg peak (“pseudo SOBP”) configuration. The graphs illustrated inFIG. 10 included simulated data for a 100 MeV electron beam with a 5centimeter radius.

All of the devices, apparatus, systems and/or methods disclosed andclaimed herein can be made and executed without undue experimentation inlight of the present disclosure. While the devices, apparatus, systemsand methods of this invention have been described in terms of particularembodiments, it will be apparent to those of skill in the art thatvariations may be applied to the devices, apparatus, systems and/ormethods in the steps or in the sequence of steps of the method describedherein without departing from the concept, spirit and scope of theinvention. All such similar substitutes and modifications apparent tothose skilled in the art are deemed to be within the spirit, scope andconcept of the invention as defined by the appended claims.

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1. An apparatus for controlling a radiotherapy electron beam, theapparatus comprising: an electron beam generator configured to generatean electron beam; a plurality of magnets producing a plurality ofmagnetic fields configured to focus the electron beam to a focal spot;and a control system configured to alter one or more parameters of theplurality of magnets to move the focal spot from a first location to asecond location, wherein the first location is located at a first depthwithin a target region and the second location is located at a seconddepth within the target region.
 2. The apparatus of claim 1 wherein: thetarget region is below an epidermal surface of a subject; and the firstlocation or the second location is at a depth between 0 and 50centimeters from the epidermal surface.
 3. The apparatus of claim 1wherein the electron beam has a energy of between 50 and 250megaelectron volts (MeV).
 4. The apparatus of claim 3 wherein the energyof the beam is not modulated when the focal spot is moved from the firstlocation to the second location.
 5. The apparatus of claim 1 wherein theplurality of magnets comprise a plurality of collinear multipolemagnets.
 6. The apparatus of claim 5 wherein the plurality of collinearmultipole magnets comprises at least two collinear quadrupole magnets.7. The apparatus of claim 5 wherein: the one or more parameters of theplurality of magnets comprises a separation distance between theplurality of collinear multipole magnets; and the control system isconfigured to alter the separation distance between the plurality ofcollinear multipole magnets.
 8. The apparatus of claim 1 wherein theplurality of magnets comprise an anterior lens magnet, a posteriorreflective magnet, and a plurality of radial focal magnets.
 9. Theapparatus of claim 1 wherein: the plurality of magnets compriseelectromagnets; the one or more parameters of the plurality of magnetscomprises an electrical current through the electromagnets; and thecontrol system is configured to alter the electrical current through theelectromagnets.
 10. The apparatus of claim 9 wherein the electromagnetsare iron-dominated or coil dominated superconducting electromagnets. 11.The apparatus of claim 1 wherein the plurality of magnetic fields areconfigured to focus the electron beam at a convergence angle of between50 and 500 mrad.
 12. The apparatus of claim 1 wherein the plurality ofmagnetic fields are configured to focus the electron beam at aconvergence angle of between 200 and 400 mrad.
 13. The apparatus ofclaim 1 wherein the control system comprises an algorithm to calculatethe one or more parameters of the plurality of magnets.
 14. Theapparatus of claim 13 wherein the control system receives input from atreatment planning software program configured to calculate a dosedistribution.
 15. The apparatus of claim 1 wherein the focal spotcomprises a maximum electron dose concentration.
 16. A method ofcontrolling a radiotherapy electron beam, the method comprising:generating an electron beam; directing the electron beam through aplurality of magnetic fields produced by a plurality of magnets;focusing the electron beam to a focal spot with the plurality ofmagnetic fields; and altering one or more parameters of the plurality ofmagnets to move the focal spot from a first location to a secondlocation wherein the first location is located at a first depth within atarget region and the second location is located at a second depthwithin the target region.
 17. The method of claim 16 wherein: the targetregion is below an epidermal surface of a subject; and the firstlocation or the second location is at a depth between 0 and 50centimeters from the epidermal surface.
 18. The method of claim 16wherein the electron beam has a power of between 50 megaelectron voltsand 250 megaelectron volts.
 19. The method of claim 18 wherein the powerof the beam is not modulated when the focal spot is moved from the firstlocation to the second location.
 20. The method of claim 16 wherein theplurality of magnets comprise a plurality of collinear multipolemagnets.
 21. The method of claim 20 wherein the plurality of collinearmultipole magnets comprises at least three collinear quadrupole magnets.22. The method of claim 20 wherein: the one or more parameters of theplurality of magnets comprises a separation distance between theplurality of collinear multipole magnets; and the control system isconfigured to alter the separation distance between the plurality ofcollinear multipole magnets.
 23. The method of claim 16 wherein theplurality of magnets comprise an anterior lens magnet, a posteriorreflective magnet, and a plurality of radial focal magnets.
 24. Themethod of claim 16 wherein: the plurality of magnets compriseelectromagnets; the one or more parameters of the plurality of magnetscomprises an electrical current through the electromagnets; and thecontrol system is configured to alter the electrical current through theelectromagnets.
 25. The method of claim 16 wherein the plurality ofmagnetic fields are configured to focus the electron beam at aconvergence angle of between 100 and 500 mrad.
 26. The method of claim16 wherein the plurality of magnetic fields are configured to focus theelectron beam at a convergence angle of between 200 and 400 mrad. 27.The method of claim 16 wherein the control system comprises an algorithmto calculate the one or more parameters of the plurality of magnets. 28.The method of claim 27 wherein the control system receives input from atreatment planning software program configured to calculate a dosedistribution.
 29. The method of claim 16 wherein the focal spotcomprises a maximum electron dose concentration.
 30. An apparatus forcontrolling a radiotherapy electron beam, the apparatus comprising: anelectron beam generator configured to generate an electron beam with apower between 50 megaelectron volts and 250 megaelectron volts; aplurality of magnets configured to focus the electron beam at a focalspot; and a control system configured move the focal spot from a firstlocation at a first depth to a second location at a second depth,wherein the power of the electron beam is maintained at a consistentlevel when the focal spot is moved from the first location to the secondlocation.
 31. The apparatus of claim 30 wherein the first location andthe second location are located within a target region.
 32. Theapparatus of claim 31 wherein: the target region is below an epidermalsurface of a subject; and the first location or the second location isat a depth between 10 and 20 centimeters from the epidermal surface. 33.The apparatus of claim 30 wherein the control system is configured toalter one or more parameters of the plurality of magnets to move thefocal spot from the first location to the second location.
 34. Theapparatus of claim 33 wherein the control system comprises an algorithmto calculate the one or more parameters of the plurality of magnets. 35.The apparatus of claim 35 wherein the control system receives input froma treatment planning software program configured to calculate a dosedistribution.
 36. The apparatus of claim 33 wherein the plurality ofmagnets comprise a plurality of collinear multipole magnets.
 37. Theapparatus of claim 36 wherein the plurality of collinear multipolemagnets comprises at least three collinear quadrupole magnets.
 38. Theapparatus of claim 36 wherein: the one or more parameters of theplurality of magnets comprises a separation distance between theplurality of collinear multipole magnets; and the control system isconfigured to alter the separation distance between the plurality ofcollinear multipole magnets.
 39. The apparatus of claim 30 wherein theplurality of magnets comprise an anterior lens magnet, a posteriorreflective magnet, and a plurality of radial focal magnets.
 40. Theapparatus of claim 30 wherein: the plurality of magnets compriseelectromagnets; the control system is configured to alter one or moreparameters of the plurality of magnets to move the focal spot from thefirst location to the second location; the one or more parameters of theplurality of magnets comprises an electrical current through theelectromagnets; and the control system is configured to alter theelectrical current through the electromagnets.
 41. The apparatus ofclaim 30 wherein the plurality of magnets are configured to focus theelectron beam at a convergence angle of between 100 and 500 mrad. 42.The apparatus of claim 30 wherein the plurality of magnets areconfigured to focus the electron beam at a convergence angle of between200 and 400 mrad.
 43. The apparatus of claim 30 wherein the focal spotcomprises a maximum electron dose concentration.
 44. A method ofcontrolling a radiotherapy electron beam, the method comprising:generating an electron beam having a power between 50 megaelectron voltsand 250 megaelectron volts; focusing the electron beam to a focal spotwith a plurality of magnets; and moving the focal spot from a firstlocation at a first depth to a second location at a second depth whilemaintaining the power of the electron beam at a consistent level. 45.The method of claim 44 wherein the first location and the secondlocation are located within a target region.
 46. The method of claim 45wherein: the target region is below an epidermal surface of a subject;and the first location or the second location is at a depth between 10and 20 centimeters from the epidermal surface.
 47. The method of claim44 wherein moving the focal spot from a first location at a first depthto a second location at a second depth comprises altering one or moreparameters of the plurality of magnets.
 48. The method of claim 47wherein the control system comprises an algorithm to calculate the oneor more parameters of the plurality of magnets.
 49. The method of claim48 wherein the control system receives input from a treatment planningsoftware program configured to calculate a dose distribution.
 50. Themethod of claim 47 wherein the plurality of magnets comprise a pluralityof collinear multipole magnets.
 51. The method of claim 50 wherein theplurality of collinear multipole magnets comprises at least threecollinear quadrupole magnets.
 52. The method of claim 50 wherein: theone or more parameters of the plurality of magnets comprises aseparation distance between the plurality of collinear multipolemagnets; and altering one or more parameters of the plurality of magnetscomprises altering the separation distance between the plurality ofcollinear multipole magnets.
 53. The method of claim 44 wherein theplurality of magnets comprise an anterior lens magnet, a posteriorreflective magnet, and a plurality of radial focal magnets.
 54. Themethod of claim 44 wherein: the plurality of magnets compriseelectromagnets; and moving the focal spot from a first location at afirst depth to a second location at a second depth comprises altering anelectrical current through the electromagnets.
 55. The method of claim44 wherein the plurality of magnets are configured to focus the electronbeam at a convergence angle of between 100 and 500 mrad.
 56. The methodof claim 44 wherein the plurality of magnets are configured to focus theelectron beam at a convergence angle of between 200 and 400 mrad. 57.The method of claim 44 wherein the focal spot comprises a maximumelectron dose concentration.